Back again in the laboratory, Kennedy threw off his coat and plunged again into his investigation of the blood sample he had taken from the wound in Mendoza's body.

We had scarcely been back half an hour before the door opened and Dr. Leslie's perplexed face looked in on us. He was carrying a large jar, in which he had taken away the materials which he wished to examine.

"Well," asked Kennedy, pausing with a test-tube poised over a Bunsen burner, "have you found anything yet? I haven't had time to get very far with my own tests yet."

"Not a blessed thing," returned the coroner. "I'm desperate. One of the chemists suggested cyanide, another carbon monoxide. But there is no trace of either. Then he suggested nux vomica. It wasn't nux vomica; but my tests show that it must have been something very much like it. I've looked for all the ordinary known poisons and some of the little-known alkaloids, but, Kennedy, I always get back to the same point. There must have been a poison there. He did not die primarily of the wound. It was asphyxia due to a poison that really killed him, though the wound might have done so, but not quite so quickly."

I could tell by the look that crossed Kennedy's face that at last a ray of light had pierced the darkness. He reached for a bottle on the shelf labelled spirits of turpentine.

Then he poured a little of the blood sample from the jar which the coroner had brought into a clean tube and added a few drops of the spirits of turpentine. A cloudy, dark precipitate formed. He smiled quietly, and said, half to himself, "I thought so."

"What is it?" asked the coroner eagerly, "nux vomica?"

Craig shook his head as he stared at the black precipitate. "You were perfectly right about the asphyxiation, Doctor," he remarked slowly, "but wrong as to the cause. It was a poison—one you would never dream of."

"What is it?" Leslie and I asked simultaneously.

"Let me take all these samples and make some further tests," he said. "I am quite sure of it, but it is new to me. By the way, may I trouble you and Leslie to go over to the Museum of Natural History with a letter?"

It was evident that he wanted to work uninterrupted, and we agreed readily, especially because by going we might also be of some use in solving the mystery of the poison.

He sat down and wrote a hasty note to the director of the Museum, and a few moments later we were speeding over in Leslie's car.

At the big building we had no trouble in finding the director and presenting the note. He was a close friend of Kennedy's and more than willing to aid him in any way.

"You will excuse me a moment?" he apologized. "I will get from the
South American exhibit just what he wants."

We waited several minutes in the office until finally he returned carrying a gourd, incrusted on its hollow inside surface with a kind of blackish substance.

"That is what he wants, I think," the director remarked, wrapping it up carefully in a box. "I don't need to ask you to tell Professor Kennedy to watch out how he handles the thing. He understands all about it."

We thanked the director and hurried out into the car again, carrying the package, after his warning, as though it were so much dynamite.

Altogether, I don't suppose that we could have been gone more than an hour.

We burst into the laboratory, but, to my surprise, I did not see
Kennedy at his table. I stopped short and looked around.

There he was over in the corner, sprawled out in a chair, a tank of oxygen beside him, from which he was inhaling laboriously copious draughts. He rose as he saw us and walked unsteadily toward the table.

"Why—what's the matter?" I cried, certain that m our absence an attempt had been made on his life, perhaps to carry out the threat of the curse.

"N-nothing," he gasped, with an attempt at a smile. "Only I—think I was right—about the poison."

I did not like the way he looked. His hand was unsteady and his eyes looked badly. But he seemed quite put out when I suggested that he was working too hard over the case and had better take a turn outdoors with us and have a bite to eat.

"You—you got it?" he asked, seizing the package that contained the gourd and unwrapping it nervously.

He laid the gourd on the table, on which were also several jars of various liquids and a number of other chemicals. At the end of the table was a large, square package, from which sounds issued, as if it contained something alive.

"Tell me," I persisted, "what has happened. Has any one been here since we have been gone?"

"Not a soul," he answered, working his arms and shoulders as if to get rid of some heavy weight that oppressed his chest.

"Then what has happened that makes you use the oxygen?" I repeated, determined to get some kind of answer from him.

He turned to Leslie. "It was no ordinary asphyxiation, Doctor," he said quickly.

Leslie nodded. "I could see that," he admitted.

"We have to deal in this case," continued Kennedy, his will-power overcoming his weakness, "with a poison which is apparently among the most subtle known. A particle of matter so minute as to be hardly distinguishable by the naked eye, on the point of a lancet or needle, a prick of the skin not anything like that wound of Mendoza's, were necessary. But, fortunately, more of the poison was used, making it just that much easier to trace, though for the time the wound, which might itself easily have been fatal, threw us off the scent. But given these things, not all the power in the world—unless one was fully prepared—could save the life of the person in whose flesh the wound was made."

Craig paused a moment, and we listened breathlessly.

"This poison, I find, acts on the so-called endplates of the muscles and nerves. It produces complete paralysis, but not loss of consciousness, sensation, circulation, or respiration until the end approaches. It seems to be one of the most powerful agents of which I have ever heard. When introduced in even a minute quantity it produces death finally by asphyxiation—by paralyzing the muscles of respiration. This asphyxia is what puzzled you, Leslie."

He reached over and took a white mouse from the huge box on the corner of the table.

"Let me show you what I have found," he said. "I am now going to inject a little of the blood serum of the murdered man into this white mouse."

He took a needle and injected some of a liquid which he had isolated. The mouse did not even wince, so lightly did he touch it. But as we watched, its life seemed gently to ebb away, without pain, without struggle. Its breath simply seemed to stop.

Next he took the gourd which we had brought and with a knife scraped off just the minutest particle of the black, licorice-like stuff that incrusted it. He dissolved the particle in some alcohol, and with a sterilized needle repeated his experiment on a second mouse. The effect was precisely similar to that produced by the blood on the first.

I was intent on what Craig was doing when Dr. Leslie broke in with a question. "May I ask," he queried, "whether, admitting that the first mouse died at least apparently in the same manner as the second, you have proved that the poison is the same in both cases? And if it is the same, can you show that it affects human beings in the same way, that enough of it has been discovered in the blood of Mendoza to have caused his death? In other words, I want the last doubt set aside."

If ever Craig startled me, it was by his quiet reply:

"I've isolated it in his blood, extracted it, sterilized it, and I've tried it on myself."

In breathless amazement, with eyes riveted on him, we listened. "Then that was what was the matter?" I blurted out. "You had been trying the poison on YOURSELF?"

He nodded unconcernedly. "Altogether," he explained, as Leslie and I listened, speechless, "I was able to recover from both blood samples six centigrams of the poison. It is almost unknown. I could only be sure of what I discovered by testing the physiological effects. I was very careful. What else was there to do? I couldn't ask you fellows to try it, if I was afraid."

"Good heavens!" gasped Leslie, "and alone, too."

"You wouldn't have let me do it, if I hadn't got rid of you," he smiled quietly.

Leslie shook his head. "Tried it on the dog and made himself the dog!" exclaimed Leslie. "I need the credit of a successful case—but I'll not take this one."

Kennedy laughed.

"Starting with two centigrams of the stuff as a moderate dose," he pursued, while I listened, stunned at his daring, "I injected it into my right arm subcutaneously. Then I slowly worked my way up to three and then four centigrams. You see what I had recovered was far from the real thing. They did not seem at first to produce any very appreciable results other than to cause some dizziness, slight vertigo, a considerable degree of lassitude, and an extremely painful headache of rather unusual duration."

"Good night!" I exclaimed. "Didn't that satisfy you?"

"Five centigrams considerably improved on it," he continued, paying no attention to me. "It caused a degree of lassitude and vertigo that was most distressing, and six centigrams, the whole amount which I had recovered from the samples of blood, gave me the fright of my life right here in this laboratory a few minutes before you came in."

Leslie and I looked at each other and shook our heads.

"Perhaps I was not wise in giving myself so large an injection on a day when I was overheated and below par otherwise, because of the strain I have been under in handling this case, as well as other work. However that may be, the added centigram produced so much more on top of the five centigrams I had previously taken that for a time I had reason to fear that that additional centigram was just the amount needed to bring my experiments to a permanent close.

"Within three minutes of the time of injection the dizziness and vertigo had become so great as to make walking seem impossible. In another minute the lassitude rapidly crept over me, and the serious disturbance of my breathing made it apparent to me that walking, waving my arms, anything, was imperative. My lungs felt glued up, and the muscles of my chest refused to work. Everything swam before my eyes, and I was soon reduced to walking up and down the laboratory floor with halting steps, only preventing falling on the floor by holding fast to the edge of the table.

"I thought of the tank of oxygen, and managed to crawl over and turn it on. I gulped at it. It seemed to me that I spent hours gasping for breath. It reminded me of what I once experienced in the Cave of the Winds of Niagara, where water is more abundant in the atmosphere than air. Yet my watch afterward indicated only about twenty minutes of extreme distress. But that twenty minutes is one period I shall never forget. I advise you, Leslie, if you are ever so foolish as to try the experiment, to remain below the five-centigram limit."

"Believe me, I'd rather lose my job," returned Leslie.

"How much of the stuff was administered to Mendoza," went on Kennedy, "I cannot say. But it must have been a good deal more than I took. Six centigrams which I recovered from these small samples are only nine-tenths of a grain. You see what effect that much had. I trust that answers your question?"

Dr. Leslie was too overwhelmed to reply.

"What is this deadly poison that was used on Mendoza?" I managed to ask.

"You have been fortunate enough to obtain a sample of it from the Museum of Natural History," returned Craig. "It comes in a little gourd, or often a calabash. This is in a gourd. It is a blackish, brittle stuff, incrusting the sides of the gourd just as if it was poured in in the liquid state and left to dry. Indeed, that is just what has been done by those who manufacture it after a lengthy and somewhat secret process."

He placed the gourd on the edge of the table, where we could see it closely. I was almost afraid even to look at it.

"The famous traveller, Sir Robert Schomburgk, first brought it into Europe, and Darwin has described it. It is now an article of commerce, and is to be found in the United States Pharmacoepia as a medicine, though, of course, it is used in only very minute quantities, as a heart stimulant."

Craig opened a book to a place he had marked. "Here's an account of it," he said. "Two natives were one day hunting. They were armed with blow-pipes and quivers full of poisoned darts made of thin, charred pieces of bamboo, tipped with this stuff. One of them aimed a dart. It missed the object overhead, glanced off the tree, and fell down on the hunter himself. This is how the other native reported the result:

"'Quacca takes the dart out of his shoulder. Never a word. Puts it in his quiver and throws it in the stream. Gives me his blow-pipe for his little son. Says to me good-bye for his wife and the village. Then he lies down. His tongue talks no longer. No sight in his eyes. He folds his arms. He rolls over slowly. His mouth moves without sound. I feel his heart. It goes fast and then slow. It stops. Quacca has shot his last woorali dart.'"

Leslie and I looked at Kennedy, and the horror of the thing sank deep into our minds. Woorali. What was it?

"Woorali, or curare," explained Craig slowly, "is the well-known poison with which the South American Indians of the upper Orinoco tip their arrows. Its principal ingredient is derived from the Strychnos toxifera tree, which yields also the drug nux vomica, which you, Dr. Leslie, have mentioned. On the tip of that Inca dagger must have been a large dose of the dread curare, this fatal South American Indian arrow poison."

"Say," ejaculated Leslie, "this thing begins to look eerie to me. How about that piece of paper that I sent to you with the warning about the curse of Mansiche and the Gold of the Gods. What if there should be something in it? I'd rather not be a victim of this curare, if it's all the same to you, Kennedy."

Kennedy was thinking deeply. Who could have sent the messages to us all? Who was likely to have known of curare? I confess that I had not even an idea. All of them, any of them, might have known.

The deeper we got into it, the more dastardly the crime against Mendoza seemed. Involuntarily, I thought of the beautiful little Senorita, about whom these terrible events centred. Though I had no reason for it, I could not forget the fear that she had for Senora de Moche, and the woman as she had been revealed to us in our late interview.

"I suppose a Peruvian of average intelligence might know of the arrow poison of Indians of another country," I ventured to Craig.

"Quite possible," he returned, catching immediately the drift of my thoughts. "But the shoe-prints indicated that it was a man who stole the dagger from the Museum. It may be that it was already poisoned, too. In that case the thief would not have had to know anything of curare, would not have needed to stab so deeply if he had known."

I must confess that I was little further along in the solution of the mystery than I had been when I first saw Mendoza's body. Kennedy, however, did not seem to be worried. Leslie had long since given up trying to form an opinion and, now that the nature of the poison was finally established, was glad to leave the case in our hands.

As for me, I was inclined to agree with Dr. Leslie, and, long after he had left, there kept recurring to my mind those words:

BEWARE THE CURSE OF MANSICHE ON THE GOLD OF THE GODS.